Harmonic frequency generator



Aug. 25, 1942. w. BENZ 2,294,067

HARMONI C FREQUENCY GENERATOR Filed Aug. 2, 1941 2 Sheets-Sheet 1 qim INVENTOR WERNER BENZ ATTORNEY Aug. 25, 1942. w. BENZ 2,294,067

HARMONIC FREQUENCY GENERATOR Filed Aug. 2, 1941 2 Sheets-Sheet 2 INVENTOR WERNER BEA/Z BY M214 ATTORNEY Patented Aug. 25, 1942 HARMONIC FREQUENCY GENERATOR Werner Benz, Berlin, Germany, assignor to General Electric Company, Schenectady, N. Y., a corporation of New York Application August 2, 1941, Serial No. 405,167 In Germany April 19, 1940 2 Claims.

In the various fields of electrical engineering, particularly in radio frequency work, circuit organizations for frequency multiplication are required. Thus, for instance, it is customary to obtain the various carrier frequencies in wired radio systems by frequency multiplication of a fundamental frequency produced in a frequencystabilized generator. Frequency multiplication also plays an important part in measuring work. For instance, in measuring the attenuation curve in filters it often is necessary that the measuring frequencies correspond exactly to the nominal or rated value. To this end various harmonics of a very constant fundamental frequency (standard frequency) are used as the measuring frequencies.

For producing a certain harmonic from a fundamental frequency the customary procedure has been to distort the fundamental frequency in a non-linear quadripole, or four-terminal network, and to separate the desired frequency by means of a suitable oscillatory circuit or filter from the plurality of harmonics which arise. Heretofore it has been assumed that the fundamental frequency should be distorted as much as possible, in other words, that the non-linear distortion should be as great as feasible.

In carrying out m invention, besides making due allowance for the considerations above mentioned, it is essential that the distorting quadripole be so designed that the non-linear distortion which is developed will serve the purpose of exalting a desired harmonic. In other words, the characteristic shall be made such that the desired harmonic will appear predominantly in the output in contrast with other harmonics which should be as much suppressed as is possible.

The invention is concerned with a circuit organization adapted to produce a certain harmonic from a fundamental frequency by distorting the said frequency by means of a nonlinear quadripole. My invention is preferably carried out by the use of a selected biasing potential which is impressed on a distorting quadripole for development of its non-linear characteristics in such a manner that with respect to a desired harmonic a high ratio is obtained between the output potential U2 and the input potential m.

The invention will noW be described in more detail, reference being made to the appended drawings in which,

Fig. 1 is a schematic diagram of a so-called quadripole circuit arrangement;

. Figs. 21, 21:, 2111, and 3 are curve diagrams which illustrate the theory of operation of my invention;

Fig. 4 shows a circuit arrangement including a distorting quadripole; and,

Fig. 5 is a circuit diagram of a preferred embodiment of my invention.

In Figure 1 is shown the fundamental circuit organization of a distorting quadripole such as may be used in the invention for producing odd harmonics, This quadripole contains in one of its series arms or branches a non-linear resistance which comprises two similar rectifiers G1 and G2 connected in parallel relationship and passing current in opposite directions. These rectifiers are biased negatively to the same degree by means of batteries V1 and V2, respectively.

As shown in Fig. 21, the preferred characteristic of the network is indicated by the relation between the values in representing the input potential and values in representing the output potential, where the quadripole is of the type shown in Fig. 1. It is clear from the delineation of curve I that a threshold value S may be determined by the impress of a certain negative bias on the network. This bias is so chosen as to suppress all output potentials U2 when the input potentials fail to rise above a certain threshold value equal to S. If the input potential ui has the sinsuoidal shape and amplitude shown by curve II, then an output potential in results which has the shape of curve III, that is to say, 'a greatly distorted curve which, as can easily be seen, comprises the fundamental and odd harmonics thereof. The same time scale is employed for curves II and Ill.

Now, in Fig. 3 the amplitudes of the various odd harmonics of the output potential are shown as a function of the threshold value for a constant input potential of amplitude l. Curve a3 corresponds to the third harmonic, curve as to the fifth harmonic, etc. It will be seen that for a threshold value of S1=.44 and 82:.79 corresponding to curve or, for instance, the seventh harmonic does not appear in the output, while for 83:22 and 84:52 the said harmonic arises with maximum intensity. Thus, for a given amplitude of the input potential there are certain values for the biasing potentials V1 and V2, for which the desired harmonic appears with maximum intensity.

Figs. 4 and 5 represent two practical exemplified embodiments for the circuit organization according to the invention.

Flg. 4 shows a distorting quadripole comprising two differential transformers T1 and T: and two similar rectifiers G1 and G2 allowing current to pass in the directions indicated by the arrows. The biasing potential (V) of both rectifiers'is fed to the mid-points of'the transformer windings facing the rectifiers. The size of the potential may be adjusted by mean of a potentiometer P1. The operation of this circuit organization is the same as that of the circuit organization shown in Fig. 1.

Of course, it is also possible to use any other suitable quadripole for the distorting quadripole, for instance, a push-pull class C amplifier in which correct setting of the threshold value of the characteristic is obtained by suitable adjustment of the grid bias of the two amplifier tubes operating in push-pull.

It can be seen from Fig. 3 that the most suitable setting of the threshold value for a given harmonic results only for a particular input amplitude. For the case that the input amplitude is not equal to the amplitude designated by I, which is the basis of Fig. 3,.the threshold value referred to amplitude i may, however, be obtained in a simple manner by dividing th actually existing threshold value, that is, for instance, the biasing potential V shown in Fig. 4, by a quantity representing the input amplitude. It will be seen that for a definite threshold value the maximum of the desired harmonic, strictly speaking, exists only for a single input amplitude, Thus, if the latter amplitude is varied, with the biasing potential remaining the same, then the ratio between the actual threshold value and the input amplitude changes; that is, the threshold value referred to amplitude l in Fig. 3 also varies.

Now, in most instances of frequency multiplication the input potential has a constant amplitude, with the result that the single adjustment of the threshold value described above completely sufilces to obtain the desired harmonic with maximum intensity. However, in instances where the inputamplitude varies, the biasing potential or the threshold value adjustment must also be changed correspondingly. Now, it is not difllcult to do this automatically by, impressing the. input potential, if necessary by way of an amplifier, upon a rectifier and by using the resulting D. C. potential for controlling the threshold value.

Fig. 5 represents an exemplified embodiment which is particularly advantageous for this case. The input potential is fed by way of a transformer T3 to an amplifier tube VI, to the plate circuit of which a distorting quadripole Z is coupled by way of transformer T4. In this distorting quadripole two rectifier paths Di and D2 serve as rectifiers, the said paths being preferably well shielded inside amplifier tube Vi from the normal triode system of the tube, The distorted potential is fed by way of the output transformer T5 of distorting means Z to a second amplifier tube V2, which also contains two rectifier paths D: and D4 besides the normal amplifier system. Included in the plate circuit of amplifier V: is an oscillatory circuit C, L1, which is tuned to the desired harmonic and from which, for instance, by way of a second winding L2 cooperating with winding Ll, the said harmonic may be taken off. A fixed negative biasing potential may beimpressed upon the rectifier paths Di and D: from a potentiometer P: included in the cathode lead of V1 by way of a resistance R. The

size of the said potential may be adjusted by potentiometer P2. Also included in the plate circuit of V1 is a transformer Ts to the secondary winding of which are connected the two rectifier paths D: and D4.

The operation of the circuit organization is such that for a certain input potential amplitude in across transformer Ta, that is, for a certain potential across transformer To, a D. C. potential is produced across resistance R which is a function of the input potential amplitude and which is added to fixed biasing potential of the distorting means Z coming from potentiometer P2. By suitable adjustment of P2 and suitable dimensioning of elements R, To, etc., conditions can be made so'that the threshold value varies in the desired manner with the input potential with the result that the most favorable threshold value automatically results for every input potential.

The embodiments hereinbefore disclosed were concerned with the production of odd harmonics of the fundamental frequency, However, the invention is not limited to this type of harmonic production. On th contrary, within the scope and sense of the invention it is possible similarly to generate even harmonics by using the basic idea of the invention. In this case the distorting four-terminal network may consist Of any wellknown type of rectifier, such as a full wave rectifier, sometimes referred to as a Graetz system.

The use of such rectifiers is combined with a source of negative biasing potential for suppressing certain of the instantaneous output potentials other than those which are developed by causing the input potentials to overcome the chosen negative bias. Just as previously for each odd harmonic, there exists in this case an' optimum value of biasing potential for each even harmonic. Similarly also, as above pointed out, the said value, if desired, may also be regulated in dependence upon the size of the input potential.

The invention may, for instance, be employed advantageously in testing work for the measurement or frequency-dependent quantities under conditions satisfactory in respect to stabilization of the nominal or rated value for the various measuring frequencies. However, it will be found useful also in multiple-carrier installations in which the various carrier frequencies are obtained by multiplication of frequency of a frequency-stabilized fundamental wave generator by the use of a distorting quadripole. In such a scheme, to be sure, a separate distorter is required for each carrier frequency; this drawback,

however, contrasted to the methods of the prior art, where only a solitary distorter is provided for the production of all of the frequencies, is more than offset because of the fact and advantage that the filter and amplifier means have to be far less elaborate. As a matter of fact, this advantage may be of relatively simple and low cost design. A further advantage to be gained is that the apparatus itself may be so standardized as to be useful in distorting the input wave differently for obtaining difierent even and-odd harmonics simply by selecting the proper biasing potential to be applied across the network, In fact such networks may differ from one another only by the biasing potential with which they are impressed. I

I claim:

1. A frequency multiplying circuit arrangement in which a desired harmonic is emphasized, comprising a source of fundamental frequency energy, an amplifier receptive of said energy, means including a full wave rectifier having input terminals connected to said source and output terminals connected across a load impedance for controlling the input circuit bias on said amplifier, a second amplifier having an output circuit tuned to said desired harmonic and having an input circuit coupled to the output side of the first said amplifier, rectification means in circuit with a bias control means for controlling the gain in the second said amplifier, and means for feeding to said rectification means an output component from the first said amplifier.

2. A circuit arrangement for exalting a definite harmonic output component with respect to a given input frequency, comprising a network having a first and a second double diode-triode discharge tube, transformer means providing intercoupling between the diode and triode sections of the first tube, a second transformer means for feeding an alternating current combined with rectified current pulses, both derived from the first said tube, to the input triode electrodes of the second tube, an output circuit for said second tube tuned to the desired harmonic, a third transformer means having a primary in the output circuit of the first tube and a secondary whose mid-tap is connected through an impedance to the cathode of the second tube, the secondary terminals being connected respectively to the two anodes in the diode section of said second tube, and a source of biasing potential effectively applied to the grid in the triode section of the second tube under control of the third transformer means in cooperation with the diode section of the second tube.

WERNER BENZ. 

